1. Field of the Invention
The present invention relates to an electric double layer capacitor and an electrolyte battery.
2. Description of the Related Art
Electric double layer capacitors are devices with excellent charge-discharge behavior.
FIG. 6 is a cross-sectional view showing a cell (2) constituting a conventional electric double layer capacitor (1), as disclosed in JP 2001-351833A, for example. In it, a pair of polarizable electrodes (20) and (21) are stacked, sandwiching a separator (6), with metal collector electrodes (3) and (30) attached to outer sides of the polarizable electrodes (20) and (21). The polarizable electrodes (20) and (21) are composed by adding a conductive polymer, such as polypyrrole, to an active carbon that is in powder or fiber form, hardening this with a bonding material, and pressure forming. The polarizable electrodes (20) and (21) are impregnated with an electrolyte such as sulfuric acid. It is also possible to use a non-aqueous electrolyte as described below instead of an aqueous electrolyte such as sulfuric acid.
A peripheral portion of the polarizable electrodes (20) and (21) is sealed by an insulating sealing member (4) composed of synthetic resin, and this sealing member (4) prevents the electrolyte from leaking out of the cell (2). Ordinarily, the cell (2) comprises two or more horizontally arrayed electric double layer capacitors (1).
When charging, one collector electrode (3) is connected to a positive side of a power source, the other collector electrode (30) is connected to a negative side of a power source, and a dc voltage is applied. Negative ions are attracted to the polarizable electrode (20) connected to the positive-side collector electrode (3), while positive ions are attracted to the polarizable electrode (21) connected to the negative-side collector electrode (3), thereby forming an electric double layer between the polarizable electrodes (3) (30).
When discharging, the collector electrodes (3) and (30) are electrically connected. The electric charge accumulated in the polarizable electrodes (20) and (21) is discharged.
Alloys containing iron, steel, nickel, and/or chrome, etc., which are conductive, have excellent mechanical strength, and are low-cost, are used for the collector electrodes.
However, there are the following problems with the electric double layer capacitor (1) described above.
The collector electrodes (3) and (30), which are made of alloys, and the sealing member (4), which is made of resin, adhere to one another due to chemical bonding between the resin and oxygen in the natural oxide film on the surface of the collector electrodes (3) and (30).
However, there may be fluctuations in the surface oxidation of alloys made of crystal grains of differing components. Therefore, there is a possibility of the electrolyte impregnated in the polarization electrodes (20) and (21) leaking from portions of weak adherence between the collector electrodes (3) and (30) and the sealing member (4), and of moisture outside the cell (2) entering the inside of the sealing member (4).
Specifically, in the case of non-aqueous electrolytes, entry of moisture from outside causes electrolysis inside the cell (2), leading to a drop in performance as an electric double layer capacitor.
The present invention has as an object to provide an electric double layer capacitor and an electrolyte battery which prevent leaking of the electrolyte and entry of moisture from outside.